//
// Copyright 2011-2015 Jeff Bush
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//


#include <stdio.h>

// Project Euler problem #11: Largest product in a grid.

int grid[20][20] = {
	8,2,22,97,38,15,0,40,0,75,4,5,7,78,52,12,50,77,91,8,
	49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,4,56,62,0,
	81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,3,49,13,36,65,
	52,70,95,23,4,60,11,42,69,24,68,56,1,32,56,71,37,2,36,91,
	22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80,
	24,47,32,60,99,3,45,2,44,75,33,53,78,36,84,20,35,17,12,50,
	32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70,
	67,26,20,68,2,62,12,20,95,63,94,39,63,8,40,91,66,49,94,21,
	24,55,58,5,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72,
	21,36,23,9,75,0,76,44,20,45,35,14,0,61,33,97,34,31,33,95,
	78,17,53,28,22,75,31,67,15,94,3,80,4,62,16,14,9,53,56,92,
	16,39,5,42,96,35,31,47,55,58,88,24,0,17,54,24,36,29,85,57,
	86,56,0,48,35,71,89,7,5,44,44,37,44,60,21,58,51,54,17,58,
	19,80,81,68,5,94,47,69,28,73,92,13,86,52,17,77,4,89,55,40,
	4,52,8,83,97,35,99,16,7,97,57,32,16,26,26,79,33,27,98,66,
	88,36,68,87,57,62,20,72,3,46,33,67,46,55,12,32,63,93,53,69,
	04,42,16,73,38,25,39,11,24,94,72,18,8,46,29,32,40,62,76,36,
	20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,4,36,16,
	20,73,35,29,78,31,90,1,74,31,49,71,48,86,81,16,23,57,5,54,
	1,70,54,71,83,51,54,69,16,92,33,48,61,43,52,1,89,19,67,48
};

int main()
{
	int startx, starty;
	int index;
	int prod1;
	int prod2;
	int prod3;
	int prod4;
	int maxprod = 0;

	for (startx = 0; startx < 20; startx++)
	{
		for (starty = 0; starty < 20; starty++)
		{
			prod1 = 1;
			prod2 = 1;
			prod3 = 1;
			prod4 = 1;

			for (index = 0; index < 4; index++)
			{
				if (startx < 16)
				{
					// Horizontal
					prod1 *= grid[startx + index][starty];
				}

				if (starty < 16)
				{
					// Vertical
					prod2 *= grid[startx][starty + index];
				}

				if (startx < 16 && starty < 16)
				{
					// right diagonal \
					prod3 *= grid[startx + index][starty + index];
				}

				if (startx > 3 && starty < 16)
				{
					// left diagonal /
					prod4 *= grid[startx - index][starty + index];
				}
			}

			if (startx < 16 && prod1 > maxprod)
				maxprod = prod1;

			if (starty < 16 && prod2 > maxprod)
				maxprod = prod2;

			if (startx < 16 && starty < 16 && prod3 > maxprod)
				maxprod = prod2;

			if (startx > 3 && starty < 16 && prod4 > maxprod)
				maxprod = prod4;
		}
	}

	printf("maxproduct is %d\n", maxprod); // CHECK: maxproduct is 70600674
}
